This invention relates to wedge-operated cutting and/or forming tools, and more particularly to an improved wedge-type drive system useful in various types of power presses.
By definition, power presses comprise apparatus for reciprocating a tool holder or platen in a work area. This motion is typically utilized to move a first tool mounted on the movable platen toward and away from a second tool mounted on a fixed platen. By this means various operations are carried out, including piercing, shearing, blanking, bending, forming, and related operations.
Various specific types of power presses have also become recognized in the art. Thus, a shear is a power press that is specifically designed to cut strip materials to length. To this end shears are almost universally adapted to move a pair of cutting blades past one another and thereby effect cutting. Typically, structure is also provided for preventing separation of the cutting blades during the cutting operation.
As opposed to a shear, a press brake is a power press adapted to perform bending and related forming operations. The tools or dies used in press brakes typically do not pass one another, so that structure for preventing separation between the tools is not required. On the other hand, the extent of separation between the tools at the closest point should be variable if the press brake is to have general utility.
A punch press is a type of power press adapted to perform a broader range of operations than is a shear or a press brake. To this end, punch presses typically incorporate structure to provide very precise control over the positioning of tools or dies throughout the reciprocatory cycle, as well as structure for varying the relative positioning of the tools at the closest point. One very common use of punch presses is in performing blanking and forming operations. Punch presses are also often utilized to perform various combinations of piercing, shearing, blanking, and forming operations, which may be carried out either simultaneously or progressively.
Heretofore most power presses have comprised a motor adapted to rotate a flywheel continuously. The flywheel is selectively coupled to an eccentric by means of a dog clutch, and the eccentric is in turn connected to a movable platen by a connecting rod. The press is actuated by tripping the dog clutch, whereby the eccentric is coupled to the flywheel for rotation through a single revolution. By this means the eccentric and the connecting rod operate to reciprocate the movable platen toward and away from a fixed platen.
At the present time the foregoing design is almost universally utilized in the manufacture of power presses. However, notwithstanding widespread usage, a number of major problems have been recognized in the design. For example, although the distance between the movable and the fixed platen at the closest point can be varied by adjusting the effective length of the connecting rod, the overall stroke of the movable platen cannot be changed without changing the eccentric of the press. The cycle time of the press also cannot be varied without changing substantially the entire structure thereof.
Another disadvantage is that once the clutch is tripped, the press must complete an operating cycle before the movement of the movable platen can be terminated. This is highly undesirable, both from a safety standpoint and from the standpoint of the possibility of damage to a very expensive set of tools should a foreign object become positioned therebetween. Perhaps the most important disadvantage to the eccentric and connecting rod type of power press is that the apparatus is very expensive to purchase. This high initial cost has literally prevented the use of shears, press brakes, and other types of power presses in various diverse types of small businesses.
The present invention comprises a novel drive system for power presses which overcomes the foregoing and other disadvantages long associated with the prior art. In accordance with the broader aspects of the invention, a wedge is supported for reciprocation by a fluid powered cylinder. The wedge is provided with a camming surface which engages a cooperating camming surface to effect reciprocation of a movable platen. By this means the wedge is adapted for actuation by the cylinder to move the movable platen toward and away from a fixed platen.
The use of the present invention provides numerous advantages over the prior art. Thus, power presses incorporating the invention may be manufactured for sale at less than one-half the price of eccentric and connecting rod power presses of similar capacity. Structure may be provided for varying both the overall length of and the terminal points of the stroke of the fluid powered cylinder. By this means not only the separation between the movable platen and the fixed platen at the closest point, but also the length of the stroke of the movable platen may be easily adjusted. Finally, the stroke of the fluid powered cylinder may be terminated at any time, regardless of whether or not an operating cycle has been completed. This is highly advantageous both from an occupational safety standpoint and from the standpoint of the ability to prevent damage to tools or dies which are actuated by the press.
In accordance with more specific aspects of the invention, the press further comprises a frame including guide portions which support the movable platen for reciprocation. The fixed platen extends between the guide portion to define one end of the work area. A backup is also provided for cooperation with the wedge to effect reciprocation of the movable platen under the action of the fluid powered cylinder.
The fluid powered cylinder preferably comprises a hydraulic cylinder. In such a case the press incorporates a self-contained hydraulic system including a hydraulic reservoir comprising part of the frame of the press. By this means the reservoir and the hydraulic fluid therein tend to add strength and rigidity to the frame, and tend to absorb vibrations which otherwise might be encountered during the operation thereof.
The hydraulic system further includes a pump which is driven by an electric motor. A solenoid controlled valve is provided for regulating the effective stroke of the hydraulic cylinder. The solenoid controlled valve is in turn operated under the control of switch structure which is responsive to reciprocation of the wedge and/or the movable platen. By this means complete control over the separation between the fixed and movable platens at the closest point and over the overall stroke of the movable platen is provided. A relief valve is also provided for terminating flow of hydraulic fluid to the hydraulic cylinder in the event that the movable platen becomes stalled. By this means any possibility of damage to the tools or dies actuated by the press is completely eliminated.